#include <bits/stdc++.h>
using namespace std;

int DP[ 1100 ];

int main()
{
int i;
int a;
int V;
int N;

	DP[ 0 ] = 0;

	cin >> N;
	cin >> DP[ 1 ];

	for( i = 2; i <= N; i++ )
	{
		cin >> V;
		a = DP[ i - 2 ] + V;
		if( a < DP[ i - 1 ] ) a = DP[ i - 1 ];

		DP[ i ] = a;
	}

	cout << DP[ N ] << endl;

	return 0;
}